Turbochargers are a type of forced induction system which deliver air to the engine intake at greater density than would be possible in the normally aspirated configuration. In general, turbochargers include a turbine housing having a turbine inlet and a turbine wheel for receiving exhaust flow from the engine exhaust manifold, as well as a compressor housing having a compressor inlet and a compressor wheel for receiving filtered air. More specifically, the flow of exhaust gases through the turbine housing drives the turbine wheel, which in turn drives the compressor wheel to draw filtered air into the compressor housing. Spent exhaust gases are extracted from an exducer of the turbine housing and through the downpipe of the vehicle exhaust system, while compressed inlet air is released through a compressor discharge and delivered to the engine intake usually via an intercooler.
The power developed by the turbine stage is a function of the expansion ratio across the turbine stage, which is the expansion ratio from the turbine inlet to the turbine exducer. The range of the turbine power is a function of, among other parameters, the flow through the turbine stage. The power generated by the turbine stage to the shaft and wheel drives the compressor wheel to produce a combination of static pressure with some residual kinetic energy and heat. By allowing more fuel to be combusted, the power that is output from a given engine can be increased without significantly increasing engine weight. Moreover, because a smaller turbocharged engine can replace larger normally aspirated engines, turbochargers also enable notable reduction in the mass and aerodynamic frontal area of the vehicle. Due to these and other advantages, turbocharger systems are repeatedly chosen over naturally aspirated arrangements, and incremental improvements for turbochargers continue to be developed.
In its most basic form, a turbocharger employs a fixed turbine housing, where the shape and volume of the turbine housing volute is determined at the design stage and cast in place. The fixed turbine housing is the most cost-effective option simply because it has the fewest parts. In one improvement, the volute is cast in place, but the volute is fluidly connected to the exducer by a duct and flow through the duct is controlled by a wastegate valve. Because the outlet of the wastegate duct is on the exducer side of the volute, which is downstream of the turbine wheel, flow through the wastegate duct is able to bypass the turbine wheel without contributing to the power delivered to the turbine wheel. In further improvements, rotating vanes, sliding sections or rings, or adjusting guide vanes are used to adjust the geometry of the turbine. Some conventional turbochargers with adjustable geometries include variable geometry turbines or turbochargers (VGTs), variable nozzle turbines (VNTs), and other turbochargers having variable geometry (VG) or variable turbine geometry (VTG).
In general, a VTG turbocharger employs adjustable guide vanes mounted to rotate between a pair of vane rings and/or one vane ring and a nozzle wall. The vanes are adjusted to control the exhaust gas backpressure and the turbocharger speed by modulating the exhaust gas flow to the turbine wheel. In many configurations, the vanes are rotated through vane lever assemblies, which are coupled to an adjustment ring, which is further rotated via a pivot shaft assembly that is linked to an actuator. As shown for example in FIG. 1, a conventional pivot shaft assembly 100 may include a pivot shaft 102, a pivot fork 104, a VTG lever 106 pivotally extending from the pivot shaft 102, and one or more bushings 108. The pivot shaft assembly shown in FIG. 1 and the lever thereof is typically required to maintain friction or press fitments that are sufficient to translate torque through the adjustment ring and to the corresponding vanes. In order to satisfy these criteria, the lever and the geometry thereof may need to be carefully formed using more costly and time-consuming processes such as metal injection molding (MIM), powder metallurgy (PM), or the like, and cannot be formed by stamping or other more cost-efficient and simple processes.
Accordingly, there is a need to provide a turbocharger with all of the benefits associated with variable geometries, but at even less cost and delay in manufacturing same. The present disclosure is directed at addressing one or more of the deficiencies and disadvantages of the prior art set forth above. However, it should be appreciated that the solution of any particular problem is not a limitation on the scope of this disclosure or of the attached claims except to the extent express noted.